As an accompaniment to conventional electronic organs, tone synthesizers responsive to a signal indicative of a nomenclature (i.e., note) associated with a highest pitch struck key on an organ keyboard have been developed. Synthesized tones are derived that are chordally and octavally related to the tone of the highest pitch struck key. Most prior art synthesizers require the musician always to depress the highest pitch key of a note grouping or chord first and release the highest pitch key last. If this technique, which many musicians find difficult to perform, is not followed, the melody effect is voiced on the note which is first depressed and jumps to the second depressed note, until the highest note of the chord has been struck. The resulting continuous jumping from note to note until the highest note of the chord is struck occurs because of the musician's inability, no matter how skilled, to depress consistently all of the keys of a chord at precisely the same time or to cause the highest pitch key of the chord to be depressed first. A similar effect occurs in reverse in response to the musician attempting, but failing, to release all of the keys simultaneously.
Systems which partially remove the keying accuracy requirement of the musician are disclosed in U.S. Pat. Nos. 3,288,904 and 3,538,804. The patented systems employ a high note guard arrangement to prevent a change in frequency of voiced sounds in the event the highest pitch struck key of a played chord is released by the musician until a new chord or highest pitch struck key of a played chord is released by the musician or a new chord or highest pitch struck key is subsequently played. The prior arrangement prevents tones associated with the highest pitch struck key from decreasing in frequency in response to release of the highest pitch struck key, a desirable feature only when the musician intends to release all of the keys approximately simultaneously. If the musician modifies the played chord to form a new chord wherein the highest depressed key is of lower tone than the previously highest depressed key, to provide a melody effect, the high note guard requires the musician to release and then depress the key which has now become the highest pitch key of the new chord. Otherwise, the melody effect of the synthesizer does not enhance the tones accompanying the new, lower pitch, highest pitch struck key. Hence, the prior art system requires the musician to develop a specific, unnatural technique for shifting from one key combination to another. Further, if the musician has released all of the depressed keys and then attempts to play another key combination, the high note guard circuit of the prior art does not eliminate the requirement for the musician to depress the highest tone key of the chord before striking any of the other keys.
In studies made in connection with development of the present invention it was discovered that the vast majority of musicians are able to depress all of the keys of a key grouping within 20 milliseconds or less and to shift from one key grouping to a second key grouping, which includes keys of the first key grouping, within 60 milliseconds. Advantage is taken of this discovery by delaying voicing of any tones associated with a new key grouping for a predetermined time period, 20 milliseconds or less. In shifting from one key grouping to a second key grouping, which includes keys of the first key grouping, coupling of tones associated with the highest struck key of the second key grouping are not voiced until approximately 60 milliseconds has elapsed from the first release of a key of the first key grouping. By delaying voicing of tones associated with the highest struck key of a grouping, the musician is not required to strike and release the keys in an unnatural manner and voicing of tones associated with keys other than the highest pitch key of a key grouping is precluded.
In accordance with a further feature of the invention, portamento is provided in response to the musician striking the keys legatissimo. Thereby, in response to a subsequent key grouping being struck while another previously struck key grouping is being voiced, wherein the subsequent key grouping has a higher pitch key than the previous key grouping, tones are smoothly shifted from frequencies associated with the highest pitch key of the previous grouping to the highest pitch key of the subsequent grouping. If the keys are activated staccatissimo, the change in frequency from one key grouping to another key grouping is in discrete steps.
In accordance with a further feature of the invention, unusual or special tones are synthesized in response to tones derived in response to the highest pitch struck key of a key grouping or in response to each change in the highest pitch struck key or noise. In response to the derived tones, tone signals having different harmonic content, represented as square waves, triangular waves and pulses are derived. The pulse widths are controlled by the highest pitch struck key within a grouping. These synthesized tones provide organs of the present invention with a wide variety of sounds and effects heretofore not previously presented on commercially available electronic organs. The unusual effects are further modified by one of or a combination of low pass, high pass, or band pass filters, having cutoff or center frequencies controlled in response to one of several parameters, and sharpness controlled by the musician.
As another feature of the invention, accurate brass tone simulation is provided. In studies made in conjunction with development of the present invention, it has been determined that there are seven major important characteristics for accurate simulation of brass tones. These characteristics are: attack rate, attack transient frequency, controlled portamento, vibrato, attack tone color change, tone color change as a function of the dynamic level of the voiced tone, and overall tone quality. It has been found that attack rate is typically composed of a pair of exponentially related, sequentially derived envelopes as the tone is being initially voiced. The effect is achieved with the present instrument by amplitude modulating tones derived in response to the highest note voices being initially sounded. It has also been found that brass tones, when initially voiced, have a tendency to be transiently flat. The flatting effect is simulated with the present invention by reducing, on a transient basis, the frequency of tones derived in response to initial striking of the highest pitch key. The amount of frequency reduction is dependent upon the highest note depressed to provide accurate simulation of initial brass voicing. It has also been found that tones derived from a brass instrument have a tendency to be frequency modulated in a random fashion at a sub-audio, vibrato rate. To this end, brass tones being voiced are frequency modulated at a sub-audio rate that varies in a random manner about a center frequency. It has also been found that during the attack phase of a brass instrument, tone color is brighter as time progresses. To this end, a variable wave shaping circuit increases the harmonic content of the voice as time progresses, for the simulated brass tones. Also, brass tone color brightness is increased as dynamic level increases, an effect attained by increasing the harmonic content of the voice with another wave shaping circuit as tone level increases.
According to a further feature of the invention, there is provided a new and improved network for simulating the characteristics of flutes. Previously, it was the general practice to simulate flutes with fixed filters or complex, expensive filters having cutoff frequencies varied in response to the input frequency thereof. In accordance with this feature of the invention, a simple, inexpensive flute filter is provided for passing the fundamental of the highest pitch key, and for rejecting harmonics, regardless of the fundamental frequency of the highest pitch struck key and of the harmonics thereof. Such result is attained by cascading a fixed, low pass filter with a variable gain amplifier, the gain of which is controlled as a direct and linear function of the nomenclature of the highest pitch struck key. Control of the gain of the amplifier is achieved in a relatively simple manner since the frequency of generated tones is controlled in response to a voltage linearly related to the highest pitch struck key, said voltage is supplied as a gain control to the amplifier.
In accordance with another feature of the invention, the attack rate of flute tones and the unusual tones may be controlled, upon the will of the musician, depending upon a selected operating mode. In a so called continuous mode, the attack rate for the flutes and unusual tones can be either relatively fast or slow. In a percussive mode, wherein tones are derived for only a predetermined time after activation of a key grouping regardless of whether the key grouping remains struck, the attack rate is always relatively fast. In both modes, the roll-off rate of certain of the flute tones, subsequent to release of the keys, is fixed. For other flute tones and the special tones, a sustain effect is provided with the organ in the percussive mode and can be provided at the will of the musician in the continuous mode.
A common aspect of many of the features is control of tone frequency and content in response to a voltage indicative of the nomenclature of the highest pitch struck key. The voltage, in addition to controlling the tone frequency of a voltage controlled oscillator (as in my copending application), provides tone content control in a simple and inexpensive manner with regard to: flatting extent, tone pulse width, flute filter amplifier gain, and, in certain instances, resonant frequency of a voltage controlled filter selectively having low pass, high pass and band pass characteristics responsive to the unusual tone sources.